This invention relates to an electronic endoscope apparatus wherein a patient circuit side and a secondary circuit side are isolated from each other.
Recently, there is extensively used an endoscope whereby an elongate insertable part is inserted into a body cavity to observe organs within the body cavity or, as required, various therapeutic treatments can be made by using a treating instrument inserted through a treating instrument channel.
There are also suggested various electronic endoscopes of a system wherein a solid state imaging device, such as a charge coupled device (CCD), is provided as an imaging means in the tip part of an insertable part and picture image information is taken out as a photoelectrically converted signal.
Now, in the case of a medical electronic endoscope, a circuit part (patient circuit) inserted into the body of a patient and a circuit part (secondary circuit) connected to a peripheral device such as a motor must be isolated from each other to prevent electrification.
FIGS. 1 to 3 show formation examples of such an electronic endoscope apparatus.
In FIG. 1, an image of an object 1 is formed on a solid state imaging device 3 by an image forming optical system 2 and a signal photoelectrically converted by this solid state imaging device 3 is transmitted to a video signal processing circuit 5 through a cable 4.
As this video signal processing circuit 5 is connected with a peripheral device such as a motor, the video signal is required to be isolated on the patient circuit side and secondary circuit side by an isolation circuit 6 within the video signal processing circuit 5.
In FIG. 2, an illuminating light output from a light source device (not illustrated) is led to a tip part 13 through a light guide 12 inserted through an electronic scope 11 and is radiated on to an object 15 through a light distributing lens system 14. The object 15 imaged by this illuminating light is formed on a CCD 17 by an image forming optical system 16. The signal photoelectrically converted by this CCD 17 is delivered to a pre-process circuit 20 forming a video signal processing circuit 19 through a signal transmitting cable 18, is pre-processed by this pre-process circuit 20, has a patient circuit and secondary circuit isolated from each other by an isolation circuit 21, is processed as determined by a post-process circuit 22, is output as a video signal as, for example, of an NTSC or three primary color signals of R, G and B and is displayed as an image by a color monitor 23 or the like.
The formation of the pre-process circuit 20 is shown in FIG. 3.
The output of the CCD 17 is amplified by an amplifier 24 to supplement the attenuation in the cable transmission and the attenuation for matching. The noise contained in the output of the CCD 17 is reduced by a noise reducing circuit 25 such as a correlated double sampler. A luminance signal Y and color difference signals R-Y and B-Y are generated by a luminance color reproducing circuit 26. These luminance signal Y and color difference signals R-Y and B-Y are input into the isolation circuit 21 and are transmitted from the patient circuit to the secondary circuit.
Now, particularly, in FIG. 2, three systems of transmitting lines are required in order to pass the luminance signal Y and color difference signals R-Y and B-Y through the isolation circuit. However, as the isolation circuit 21 must stably pass a high frequency signal and is expensive, if it is provided in each of the three systems, the cost will increase. Therefore, in order to reduce the cost, it is necessary to reduce the number of transmitting lines.
It may be possible isolate the circuits at a point forward of the luminance signal reproducing circuit 26. However, if the isolation between the patient circuit and secondary circuit is made forward of the circuit 26 the high frequency CCD 17 driving pulse, color demodulating pulse and correlated double sampling pulse will have to be transmitted through the isolation circuit. However, in the transformer used as the isolation circuit, as the high frequency component attenuates, no positive sampling will be made. If the phase of the color demodulating pulse slips, the color signal level will be reduced and, if the phase of the correlated double sampling pulse slips, the S/N of the video signal will be deteriorated. Therefore, for the above mentioned reasons, in case a high frequency pulse is passed through the isolation circuit, due to the delaying characteristic dispersion and temperature fluctuation, the picture quality will likely be deteriorated.
Particularly, when transmitting a timing pulse from the patient circuit side to the secondary circuit side, the reference clock will be of a high frequency usually above ten or more MH, and therefore a high frequency transformer or high speed photocoupler satisfying this band will be required for the isolation device.
Between the patient circuit side and the secondary circuit side, the isolation pressure-proofness is required to be high to meet the safety standard.
Therefore, a large expensive transformer or an expensive photocoupler having no space in the pressure-proofness must be used.